Make the pie crust by combining all-purpose flour and kosher salt in a food processor. Cut in the unsalted butter until the mixture resembles pea-sized crumbs. Gradually add ice water until the dough comes together. Shape into a disc, wrap, and chill.

Par-bake the crust by preheating your oven to 375°F (190°C). Roll out the chilled crust and fit into a pie plate. Freeze for 15 minutes, dock with a fork, fill with weights, and bake for 15 minutes. Remove weights and bake for an additional 5 minutes until lightly golden. Cool on a wire rack.

Prepare the filling by lowering the oven to 325°F (163°C). Whisk together apple butter, eggs, dark brown sugar, and vanilla until smooth. Gradually mix in sweetened condensed milk until fully combined.

Bake the pie by pouring the filling into the cooled crust. Bake for 30 minutes, shift to the bottom for an additional 10-15 minutes. The custard should be slightly jiggly in the center. Cool on a wire rack.

Cool and top by whipping the heavy cream, powdered sugar, cinnamon, and vanilla until stiff peaks form. Spread over the cooled pie, drizzling extra apple butter on top if desired.

Slice and serve the pie at room temperature or chilled, enjoying with friends and family.